This invention relates generally to gas turbine engines, and more specifically to gas turbine engine assemblies and methods of assembling the same.
At least some known gas turbine engines include a fan, a core gas turbine engine, and a power or low-pressure turbine. The core engine includes a high-pressure compressor, a combustor, and a high-pressure turbine that are coupled together in a serial flow relationship. The low-pressure turbine is coupled downstream from, and driven by, the core gas turbine engine. More specifically, the high-pressure compressor and the high-pressure turbine are coupled together using a first shaft to define a high-pressure rotor assembly, and the low-pressure turbine and the fan are coupled together using a second shaft. Air entering the core engine is mixed with fuel and ignited to form a high energy gas stream. The high energy gas stream is discharged through the high-pressure turbine to drive the high-pressure turbine and thus also drive the low-pressure turbine.
To reduce life-cycle maintenance costs, gas turbine engines under design consideration include a high-pressure turbine disk that has a bore diameter that is substantially smaller than the bore diameter of known high-pressure turbine disks. Utilizing a high-pressure turbine disk having a relatively small bore diameter may result in an increase of the disk life by reducing disk stress. Specifically, the core gas turbine engine is sized to accommodate the high-pressure turbine disk. While sizing the high-pressure turbine disk may increase the life of the disk, the core gas turbine engine must still be designed to have an acceptable speed margin between operating speed and the first critical.
However, while design considerations provide for a core gas turbine engine that is capable of operating at a much higher speed than at least some known core engines, it is difficult to design a gas turbine engine that meets both the high-pressure turbine disk life requirements, and also meets the speed margin criteria. Specifically, the smaller diameter high-pressure turbine disk bore results in a reduced diameter drive shaft between the low-pressure turbine and the fan. As a result, this drive shaft may experience bending or torque levels that are also not acceptable to meet design criteria.